[Leetcode] Permutations

Given a collection of numbers, return all possible permutations.

For example,
[1,2,3] have the following permutations:
[1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], and [3,2,1].

注意for循环的其实条件。

用swap为了方便、简洁。

class Solution {
public:
    vector<vector<int> > permute(vector<int> &num) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() 
        vector<int> answer;
        vector<vector<int> > result;
        dfs(result,answer,num,0);
        return result;        
    }
    
    
    void dfs (vector<vector<int> > &result, vector<int> &answer, vector<int> &num, int depth)
    {
        if(depth==num.size())
        {
            result.push_back(num);
            return;           
        }
        
        for(int i=depth;i<num.size();i++)
        {
            swap(num[depth],num[i]);
            dfs(result,answer,num,depth+1);
            swap(num[depth],num[i]);
        }
    }
};